As is known, oxygen is the most abundant element in nature. It forms part, in a proportion of approximately 21%, of the atmosphere it is found forming part of most minerals and rocks and, of course, is a constituent of all living beings.
In the specific case of animals, oxygen is essential for ensuring organic metabolism, which, in superior vertebrates, and therefore man, takes place through breathing, which consists in the inhalation of atmospheric oxygen through the lungs and the subsequent transport through the bloodstream. As it is a basic life-supporting element it is not surprising that, when considered as a product, oxygen is also essential in manifold medicinal applications. It is therefore essential in many medical processes which require this element as an agent to speed up metabolism. Oxygen therapy and air therapy are well known examples. Oxygen is also used in anesthesia, as well as in open heart surgery, where the patients blood must be directly oxygenated.
In short, it may be said that oxygen is nowadays an essential medical product which may not be lacking in any hospital and which is consumed in far from negligible amounts.
In order to ensure this supply and to enable its distribution throughout the hospital complex, there is a supply station which distributes the product throughout the hospital through an internal distribution network. The supply station is usually composed of by steel cylinders (bottles) which contain the gas under pressure or, more recently, by cryogenic tanks which store liquid oxygen at low temperature and, after vaporization in a heat exchanger, the oxygen is supplied to the hospital network. All the stations have corresponding emergency systems, constituted by a set of bottles which act as a reserve and enter into operation in case of need should the main source suffer a serious breakdown or should there be no supply.
Medicinal oxygen supplied in this way is an expensive product. Its price is determined by two essential factors.
In the first place, it is necessary for its purity to be high, approximately 99.9%, since it is generated in chemical plants with a basic production destined for industrial uses. It is also essential to ensure that the quality of the product sent for hospital consumption is not in any way polluted.
Secondly, consumption of the product by an average hospital, is considerably smaller than in industrial consumption, although the installations required for its storage, and specifically in the case of cryogenic tanks, have similar and considerably high costs, wherefore they have a more significant effect in the price of medicinal oxygen.
It is also necessary to point out that the medicinal application of pure oxygen is practically non-existent. In fact, pure oxygen is a highly toxic product and the continued inhalation thereof causes death. It therefore is normally supplied with air or other gases in variable concentrations of oxygen which very rarely exceed 80%. Most frequently, the oxygen product is provided in a proportion of around 40%. For this reason, American Pharmacopoeia has just authorized the classification of medicinal oxygen as oxygen which does not have an impurity of inert gases of over 7%, and therefore a concentration of oxygen equal to or over 93%.
On the other hand, as previously mentioned, oxygen is a very abundant element, for it is present as such in the atmosphere in a very high proportion, the other components of air being nitrogen and a very small part of argon, apart from traces of other gases.
The possibility of "filtering" air, separating its constituents, was achieved some years ago by means of zeolite filters or membranes, which absorb a gas (generally nitrogen) and allow the rest to pass through. Thus oxygen may be produced, in situ, with a considerably low cost, for only a system of compressors and filters are necessary to produce it, with a reduced maintenance and a likewise low consumption of energy.
The main disadvantage of these units consists in the fact that they cannot produce oxygen with a purity of over 95%, has been eliminated with the mentioned recent authorization of American Pharmacopoeia. The required 93% purity is easily obtained with the main remaining impurity being the inert gas argon.
There is however a further disadvantage in connection with reliability.
It is wholly unthinkable that a hospital may be deprived of the oxygen supply. This condition must be avoided at all costs and any supply system must absolutely prevent this. Autonomous generating units are not satisfactory because they are machines, and as such, are subject to possible breakdowns and stoppings.
It is true that, by duplicating some parts of the system, it is possible to decrease the risk of stopping, but, apart from the fact that total elimination of the risk thereof is impossible, successive accumulation of duplicate or safety elements make the costs of these units so high that the oxygen produced no longer has economic advantages.